1. Field of the Invention
The present invention relates to computer fans, and particularly to a circuit for controlling rotation speed of a computer fan.
2. Description of Related Art
Generally, a computer system includes a motherboard with various chips such as a central processing unit (CPU) mounted thereon, a storage device such as a hard disc, and input/output devices. Many of these devices generate heat when the computer system is operating, particularly the CPU. If the heat generated from the CPU is not dissipated in a timely fashion, it may damage the CPU or even other parts of the computer system.
Typically, a sensor is programmed to be used as a temperature detector for detecting the temperature of the CPU. A computer fan is used to facilitate removal of heat to keep the temperature of the CPU within a safe range. A fan controller is provided to adjust the fan speed to be more energy efficient while still providing enough heat dissipation. Two common kinds of computer fans are 3-pin fans and 4-pin fans. The fan speed of a 3-pin fan can be adjusted by changing a voltage signal (power signal) input to the 3-pin fan. The changed voltage signal corresponds to a change in a first pulse-width modulation (PWM1) signal output by a basic input/output system (BIOS) of the motherboard. The fan speed of a 4-pin fan can be adjusted by a second pulse-width modulation (PWM2) signal output by the basic input/output system (BIOS) of the motherboard directly to the 4-pin fan.
In a 3-pin fan motherboard, a 3-pin fan is connected to the motherboard by a 3-pin header mounted on the motherboard, and a 3-pin fan controller is used to provide the voltage signal to the 3-pin fan for adjusting the rotation speed of the 3-pin fan. In a 4-pin fan motherboard, a 4-pin fan is connected to the motherboard by a 4-pin fan header mounted on the motherboard, and a 4-pin fan controller is used to provide the PWM signal to the fourth pin of the 4-pin fan for adjusting the rotation speed of the 4-pin fan. In theory, the 3-pin fan can be connected to the 4-pin fan motherboard by the 4-pin header. However, the 3-pin fan cannot be controlled by the 4-pin fan controller because the 3-pin fan does not have the fourth pin and cannot receive the PWM signal from the 4-pin fan controller. Therefore, the CPU of the 4-pin fan motherboard may be damaged because the heat may not be dissipated properly.
What is needed, therefore, is a means for adjusting the rotation speed of a computer fan, whether the computer fan be a 3-pin fan or a 4-pin fan.